1 . Field of the Invention
The present invention relates to a filter unit for an intake air for a gas turbine, which is designed to remove atmospheric dusts, whereby the deposition of the dusts in an air compressor or the like in a gas turbine plant can be alleviated, thereby preventing a reduction in power-generating output and ensuring that it is unnecessary over a long period to carry out the washing or cleaning of the air compressor and the like and the replacement of a filter, and more particularly, to a high-performance filter for an intake air for a gas turbine and a filter unit using such high-performance filter for an intake air for a gas turbine, which can be placed in a reduced space.
2. Description of the Related Art
As shown in FIG. 8, a gas turbine a draws the open air b during operation thereof. Atmospheric dusts such as fine dusts, rainwater, mists, fine carbon particles in an exhaust gas, salt particles and the like are in suspension in the open air b, Therefore, there is encountered a problem such atmospheric dusts cause the corrosion and pollution of the inside of the gas turbine, and are deposited particularly on an air compressor c to produce a reduction in performance of the air compressor c to reduce the power-generating output. To previously prevent the drawing-in of the atmospheric dusts, a dust collector or a filter unit e for mechanically separating off the atmospheric dusts from the air to clean the air is placed in an air intake port d in the gas turbine a. The filter unit e is formed into two stages of a coarse filter f made of a rolled band-shaped type glass fiber material, and a medium-performance filter g comprising an ion-exchange fiber filter formed into a folded-type, as disclosed in Japanese Patent Application Laid-open No. 5-106464.
In FIG. 8, reference character h designates a turbine section of the gas turbine, and reference character i designates a generator driven by the gas turbine a. In the conventional filter unit for the intake air for the gas turbine, it is impossible to sufficiently remove the atmospheric dusts and hence, a reduction in power-generating output from the gas turbine is produced. In addition, the conventional filter unit is of a small dust holding capacity and hence, it is necessary to replace the filter frequently, e.g., 2 to 3 times a year. For this reason, it is desired to propose a high-efficiency and long-life filter unit for an intake air for a gas turbine, which cannot cause a reduction in power-generating output and in which the filter is only required to be replaced at the time of a regular inspection of the gas turbine obliged to be carried out one time a year.
The present inventors have proposed a filter unit of a four-stage type comprising a panel-type demister or a weather louver, a rolled band-shaped type or blow-through type pre-filter, a box-shaped medium-performance filter, and a box-shaped high-performance filter to meet the above demand. However, such filter unit suffers from a problem that its size is increased, resulting in a widened placement space and an increased equipment cost and hence, a countermeasure is required. Therefore, the present inventors have reached a conclusion that a medium-performance filter and a high-performance may be used in combination from the viewpoints of a low pressure drop, a high efficiency and a long life, and they have referred to prior art techniques concerned with the combination of filters. However, each of such prior art techniques has a problem. More specifically, it is disclosed in Japanese Utility Model Application Laid-open No. 562-132715 that for the purpose of reducing the space for placement of a filter unit, a filter paper having a predetermined collection efficiency is placed at a location downstream in a direction of a air flow within a casing, and filter papers having a collection efficiency lower than that of the downstream-side filter paper are placed at multiple stages at a location upstream of the downstream-side filter paper. However, the filter is not reduced in size and hence, it is impossible to achieve the purpose of reducing the placement space.
It is disclosed in Japanese Utility Model Publication No. H3-35373 that for the purpose of removing salt particles, a spacer having voids is interposed between two filter media having a water-repellency. The arrangement of such filter is intended to ensure that even if the salt particles are converted into liquid drops, the liquid drops are permitted to be dropped along a back of the filter media located on an upstream side. However, the thickness of the filter media is increased, and the area of the filter media cannot be increased in order to provide a life of 8,000 hours or more, and additionally, the pressure drop is increased.
It is disclosed in Japanese Patent Application Laid-open No. 554-94176 that for the purpose of provide a high efficiency of filtration (0.1 xcexcm DOP) of 99.99% or more (so-called ULPA), a filter is formed in two layers, namely, a filter media having an filtration efficiency of 99.97% or more for particles having a particle size of 0.3 xcexcm is disposed as the layer downstream in a direction of a air flow, and a filter media having a filtration efficiency lower than 99.97 and equal to or higher than 75% for particles having a particle size of 0.3 xcexcm is disposed as the upstream layer, and the two filter media are folded in a zigzag fashion in closely superposed states. In this case, the filter is formed in the two layers from the viewpoints of the limitation of size and the ease to make, as compared with a filter unit formed at two stages. In this filter, however, it is an object to provide a high efficiency, but the life is not taken into consideration. When the filter is used in a gas turbine, the filter is clogged earlier and hence, it is necessary to carry out the replacement of the filter two or three times a year.
Therefore, in order to solve the above-described problems, the present inventors has proposed a high-performance filter for an intake air for a gas turbine, as disclosed in Japanese Patent Application Laid-open No. 7-253029, in which a low-efficiency filter media and a high-efficiency filter media are superposed closely on each other from an upstream side in a direction of a air flow, each of the filter media being formed with a filtering area of 25 to 35 m2, so that the filter media having a filtration efficiency of 10 to 70% for particles having a particle size of 0.3 xcexcm is disposed as a layer upstream in the air flow direction, and the filter media having a filtration efficiency of 90 to 99.99% for particles having a particle size of 0.3 xcexcm is disposed as a downstream layer.
For atmospheric dusts used for the first estimation of the filter, an excellent effect indicating a life of 8,000 hours or more has been provided. However, when the re-estimation of the filter has been carried out using other atmospheric dusts, it has been made clear that the pressure drop in the filter unit has been suddenly increased after lapse of about 4,300 hours, resulting in a shorter life. This is because the concentration of the fine dusts having the typical particle size of 0.3 xcexcm is as very high as about 5 times that of the dusts used in the first estimation and for this reason, the load has been concentrated on the downstream layer.
Accordingly, it is an object of the present invention to provide a filter for an intake air for a gas turbine and a filter unit using such filter for an intake air for a gas turbine, which can be placed in a reduced space, wherein even if the filter unit is used for high-concentration fine atmospheric dusts having a typical particle size of 0.3 xcexcm, a life of 8,000 hours or more can be ensured, and a reduction in power-generating output can be prevented by alleviating the deposition of the atmospheric dusts in an air compressor or the like in the conventional gas turbine plate, thereby ensuring that it is unnecessary over a long period of time to carry out the washing or cleaning of the air compressor or the like and the replacement of the filter.
To achieve the above object, according to a first aspect and feature of the present invention, there is provided a high-performance filter for an intake air for a gas turbine, comprising a low-efficiency filter media and a high-efficiency filter media superposed closely on each other in the named order from an upstream side in a direction of a air flow, each of the filter media being formed with a filtering area of 20 to 35 m2, so that the filter media having a filtration efficiency of 40 to 70% for particles having a particle size of 0.3 xcexcm is disposed as a layer upstream in the air flow direction, and the filter media having a filtration efficiency of 90 to 99.99% for particles having a particle size of 0.3 xcexcm is disposed as a downstream layer.
The filter media may be folded in a zigzag fashion such that they are corrugated in a direction substantially perpendicular to the direction of the air flow, and preferably, a separator formed of a sheet folded in a corrugated shape may be inserted into each of grooves resulting from the folding of the filter media, the separator being tapered in such a manner that the height of corrugation at a trailing end of the separator in an inserting direction is larger than that at a leading end of the separator. However, the filter media are not limited to the separator type, and may be of a mini-pleat type or a double-pleat type.
In addition, according to a second aspect and feature of the present invention, there is provided a filter unit for an intake air for a gas turbine, comprising dust-removing filters mounted at a plurality stages, the dust-removing filters being a panel-type demister or a weather louver, a rolled band-shaped type or blow-through type pre-filter, and a high-performance filter for an intake air for a gas turbine according to the first feature, respectively, in the named order from an upstream side in a direction of a air flow.
In the above filter unit according to the present invention, the pre-filter nay be of a blow-through type with a filtering area of 2 to 8 m2.
The panel-type demister constituting the filter unit for the intake air for the gas turbine serves to prevent the entrance of rainwater and is conventionally well-known. An example of the panel-type demister conventionally known is a demister made by curling an animal or vegetable fiber and a synthetic fiber into a spring-like state to produce a large number of elastic masses, laminating and bonding the elastic masses to one another by a binder to provide a plate, and encapsulating such plate within a frame. This demister generally has a thickness of 10 to 50 mm and a filtration efficiency (according to JIS Z 8901 test dust No. 8 colorimetric method) of 15 to 60% at a wind velocity 2 m/sec, and indicates a pressure drop of 10 to 100 Pa. Such demister has a feature that the pressure drop is smaller, i.e., a draft resistance is smaller, and a filtering efficiency for water drops is higher. When the demister has been soiled, it may be removed from the frame and washed, whereby the demister can be reused. Of course, a folded-type weather louver formed to prevent the entrance of rainwater by a folded passage can be used in place of the above-described panel-type demister.
The pre-filter constituting the filter unit for the intake air for the gas turbine according to the present invention is of a rolled band-shaped type or a blow-through type. In the rolled band-shaped type, as shown in FIG. 2, a band-shaped filter media 10 made of a glass fiber material is stretched to block an intake air passage 11, and a feed roller 12 having the filter media therearound is placed at an upper location. On the other hand, a take-up roll 13 for taking-up the filter media 10 fed from the feed roller 12 is placed at a lower location. The rolled band-shaped pre-filter is generally made of a material comprising a non-woven fabric made using a glass fiber, a polyester fiber or the like, and has a thickness of 20 to 70 mm, an average fiber diameter of 15 to 60 xcexcm, a pressure drop of 40 to 80 Pa at a wind velocity of 2.5 m/sec, a filtering efficiency (according to JIS Z 8901 test dust No. 15, mass concentration measurement method) of 60 to 90% and a dust holding capacity of 500 to 1,300 g/m2.
However, when the rolled band-shaped type is used, the maintenance of a taking-up drive device is required and hence, in order to form the pre-filter into a complete maintenance-free type, the blow-through type having a widened filtering area is preferred.
In the blow-through type, as shown in FIGS. 3 to 5, a filter media 20 is formed into a shape with a large number of bags 21 mounted continuously, and is attached by screws 26 to a frame 25 through a head portion 24 having a plurality of crosspieces 23 and matched to an opening 22 of the filter media 20.
The filter media of these pre-filter is made of a material comprising a dry non-woven fabric of an organic fiber such as polyester, acryl and the like, and has an average thickness of 5 to 25 mm, an average fiber diameter of 5 to 60 xcexcm, basis weight of 50 to 600 g/m2, a pressure drop of 20 to 300 Pa at a wind velocity of 2.5 m/sec, and an efficiency (according to JIS Z 8901 test dust No. 15, mass concentration mesurement method) of 60 to 99%. The blow-through type pre-filter having a filtering area of 2 to 8 m2 and an outer size of Length (L) 592 mmxc3x97Wide (W) 592 mmxc3x97Depth (D) 500 mm is made using this filter media. However, the shape of the blow-through type pre-filter is not limited, and the blow-through type pre-filter may be of any shape ensuring that a desired filtering area can be provided.
If the filtering area is smaller than 2 m2, a desired life of the filter unit is not obtained. If the filtering area exceeds 8 m2, the pressure drop is higher and hence, such a filtering area exceeds 8 m2 is not preferred. Therefore, the filtering area is preferable to be in a range of 2 to 8 m2. 
The performance of this filter is such that a pressure drop at an air flow rate of 50 m3/min is 20 to 80 Pa, an efficiency (according to JISz8901 test dust No. 15, mass concentration mesurement method) is 60 to 99%, and a dust holding capacity is 500 to 4,000 g.
The high-performance filter for the intake air for the gas turbine according to the present invention is made using the combination of a low-efficiency filter media and a high-efficiency filter media. It is preferable to use a high-performance filter media having a filtration efficiency of 90 to 99.99% for particles having a particle size of 0.3 xcexcm.
The reason is as follows: If the particle size is lower than 90%, it is impossible to prevent the deposition of dusts in a compressor in the gas turbine. If the particle size exceeds 99.99%, it is effective for preventing the deposition of dusts, but problems of an increase in pressure drop and a reduction in life are arisen.
It is preferable to use a low-efficiency filter media having a filtration efficiency of 40 to 70% for particles having a particle size of 0.3xcexcm. The reason is as follows: If the particle size is lower than 40%, as in a case of atmospheric dusts including fine dusts of high-concentration typically having a particle size of 0.3 xcexcm, the burden on the high-efficiency filter media located at the downstream location is increased. If the particle size exceeds 70%, a problem of early clogging of the filter media is arisen.
The high-efficiency filter media 30a and the low-efficiency filter media 30b are closely superposed on each other and folded in a zigzag fashion, so that they are corrugated it the direction substantially perpendicular to the direction of flowing of the intake air in order to increase the filtering area. The filter media are incorporated into a frame 31 with a seal material 32 interposed therebetween, and a separator 33 formed of a sheet folded in a corrugated shape is inserted into each of grooves resulting from the folding of the filter media.
By using a so-called inclined separator formed into a tapered shape with a height H1 of corrugation at a trailing end in an inserting direction being larger than that H2 at a leading end in the inserting direction, the filter can be made to have a high performance at a larger air flow rate, as compared with the use of a separator having a height of corrugation uniform over the entire length as in a case of a usual separator.
In such high-performance filter, in general, the total thickness of the filter media is in a range of 0.4 to 2.0 mm: basis weight is in a range of 100 to 200 g/m2; the pressure drop at a wind velocity of 5.3 cm/sec is in a range of 50 to 450 Pa: and the efficiency (0.3 xcexcm DOP) is in a range of 90 to 99.9%. The separator is made of a material such as a foil of metal such as aluminum, stainless and the like, a sheet of paper such as a craft, a synthetic fiber and the like, a synthetic resin film such as a polyarylate, a polyethylene-terephthalate and the like. The filter media are folded in the zigzag fashion, and the separator is inserted into each of the grooves resulting form the folding of the filter media. When the high-performance filter made in the above manner has an outside size of L610 mmxc3x97W610 mmxc3x97D290 mm, it has a filtering area in a range of 25 to 35 m2. When the filter has an outside size of L594 mmxc3x97W594 mmxc3x97D290 mm, it has a filtering area in a range of 20 to 30 m2. If the filtering area is smaller than 20 m2, the pressure drop is higher, resulting in a shorter life. If the filtering area exceeds 35 m2, a problem that the spacing between the filter media cannot be maintained is encountered. Therefore, it is preferable that the filtering area is in a range of 20 to 35 m2.
The performance of this filter is such that a pressure drop at an air flow rate of 50 m3/min is in a range of 150 to 450 Pa; an efficiency (0.3 xcexcm DOP) is in a range of 90 to 99.99%, and a dust holding capacity is in a range of 1,000 to 3,000 g.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.